The present invention relates to indicators that provide information to consumers about the extent of use of consumable air-treatment products. More specifically, it relates to air treatment dispensing devices where a heater causes dispensing of an air treatment chemical and also initiates a use-up cue system that is in the form of a multiple dye indicator.
A variety of prior art devices are known that use heat to dispense air treatment chemicals. For example, it is known that a porous pad, wick, or other substrate can be impregnated or coated with a volatilizable air treatment chemical. When heat is applied to the substrate, the air treatment chemical is dispensed into the air.
In some of these devices a portion of the substrate is dipped into an associated reservoir of the air treatment chemical (typically a mix of solvent and volatile treatment chemical). The porous substrate then acts as a wick that draws the chemical to the heated region, as needed.
The level of the air treatment chemical/solvent mix in the reservoir is typically visible to consumers. Thus, the emptying of the reservoir provides a way for consumers to monitor when more air treatment chemical is needed. However, for some applications it is preferred not to have to use the somewhat bulky storage reservoir. Further, that type of reservoir system may have certain other disadvantages besides size (e.g. cost).
Hence, the art has developed a variety of porous materials that are impregnated at a factory with air treatment chemicals. They are then positioned adjacent to or on a heater, and the heating dispenses the air treatment chemical into the air from the substrate (by vaporization and/or with assistance of a fan or the like). However, the heating of such a substrate does not typically significantly change the appearance of the substrate, particularly when the substrate is a solid rather than a gel.
Thus, producers of such products will often estimate average useful life of such products under normal usage conditions, and note that information on their packaging. However, these substrates may be used with a variety of different types of heaters which heat at different temperatures or in different ways. Even where only a single type of heater is to be used with a particular type of substrate, heater performance may be inconsistent over time.
While estimated averaging of useful life can provide rough guidance regarding useful life, that estimate will not be exact in most cases. As a result some companies prefer to provide useful life information to consumers in a manner that encourages the product to be thrown away somewhat earlier than the average statistical life. This reduces the risk that there will be significant use of the product after the product has become ineffective, albeit at the cost of a somewhat higher level of waste due to disposing of some product which still has some useful life.
Even where information is provided by the manufacturer regarding expected useful life, some consumers will not learn of, or alternatively not apply, that information. Rather, they will assume what an appropriate useful life is or should be, and thus in some cases prematurely throw away the product, and in others use it after its effective life is over. Further, even where the consumer is initially aware of the appropriate assumption for a usage life, they may forget about the need to replace the product until well after the product has become ineffective.
There are a number of automatic use-up cue systems which have been developed and applied in varied contexts which rely on some form of chemical reaction to cause an automatic color or other visible change after use for a specified period. See e.g. U.S. Pat. Nos. 4,987,849 and 6,787,108. However, systems of this type are difficult to reliably apply in a heated environment, particularly where the exact heat conditions that the product will be exposed to is not controllable or predictable. This is particularly important because chemical reactions typically proceed at very different speeds depending on the environmental temperature.
Some other known indicator devices rely on the migration of a dye to a visible position as an indicator of the extent of use. See e.g. U.S. Pat. Nos. 4,212,153, 4,903,254 and 6,701,864. However, these devices typically require consumer intervention to initiate the dye migration, and sometimes require complex structures to control use of the dye. They thereby unnecessarily increase the cost of the indicator and may also reduce the likelihood of consumer acceptance, particularly where the manner of using the product is not conceptually straightforward.
Other patents which exemplify the general status of knowledge in this art include U.S. Pat. Nos. 4,293,095 and 6,524,000.
Thus, there is still a need in the art to have improved use-up cue systems for heated volatile dispensers which do not rely on viewing liquid levels in a reservoir and can adjust for varied heating conditions.